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PubMed2004

Cultural influences on the development of lateral preferences: a comparison between French and Tunisian children.

We compared the development of laterality in two cultures that differ in pressure against left-handedness. Tunisian children, who are discouraged by their parents from using their left hand for all food-related activities, were compared to French children, who are allowed to use either the left or right hand. The subjects were 5, 7, and 9 years of age. To check the development of laterality, we tested hand preference (for writing and for performing 14 other manual activities), right-left performance difference, eye preference, and foot preference. The results showed that the frequency of left-handedness and left-eyedness was lower among Tunisian than among French children; this was particularly clear at age 5. Group difference almost disappeared in primary school children. Footedness did not differ between the two groups. Tunisian right-hand writers, although they probably included some children who might not have been right-handed without the cultural pressure, were not less consistent than French right-hand writers on the 14-item scale; they even showed a greater performance difference in favour of the right hand than the French on the pegboard task. These results may indicate that cultural pressure influences handedness at an early age, perhaps by leading towards right-handedness in children whose genetic background might otherwise have induced a chance-determined pattern of handedness.

Child↗

PubMed2005

Chimpanzees are right-handed when recording bouts of hand use.

Whether nonhuman primates exhibit population-level handedness remains a topic of considerable debate. Previous research has shown that chimpanzees are right-handed when frequencies of hand use are recorded but some have questioned the validity of this approach. In this study, we evaluated handedness in 180 captive chimpanzees for a task measuring bimanual actions. Bouts rather than frequency of hand use were recorded in each subject. Population-level right-handedness was found using both continuous and nominal scales of measurement. Neither sex nor rearing history had a significant effect on hand use. These results indicate that chimpanzees are right-handed, even when using a more conservative measure of handedness. Limitations in the use of bouts in handedness assessment are also discussed.

Animal Population Groups↗

PubMed2006

Do left-handed children have advantages regarding school performance and leadership skills?

A handedness polymorphism exists in all human populations so far investigated, at least since the Palaeolithic. Handedness is a heritable trait, and a possible evolutionary explanation for the higher prevalence of right-handers is the association of left-handedness with some deleterious traits. In this context, the persistence of left-handers remains unexplained. Reproductive success has been shown to be dependent on cultural success in many human societies. This study is the first attempt to consider the importance of social status to evolutionary processes related to handedness. We conducted a survey in French public primary schools to look for a possible association between laterality, school performance, and leadership skills. This study revealed only weak associations, and a sex effect. For primary-school girls, we report a negative association between several indicators of left-sidedness and teacher's ratings of school performance and leadership skills. For primary-school boys, we report a positive association between left-handedness for writing and teacher's ratings of school performance. The present study did not reveal any strong relation between laterality and school performance, but has shown that general school performance is not independent of laterality, and that the effect is opposite in males and females. The main difficulty is now to define clearly the different intellectual functions involved.

Biological Evolution↗

PubMed2001

Testosterone and grasp-reflex differences in human neonates.

According to the Geschwind-Behan-Galaburda (GBG) hypothesis, prenatal testosterone (T) causes a slowing in the development of the left brain with a consequent compensatory growth in the right brain, creating a reverse organisation of the cerebral lateralisation. That is, left- and right-handedness might be associated with high and low prenatal T levels, respectively. To test this hypothesis, the relations of T levels (umbilical cord blood) to grasp-reflex strengths were studied in human neonates. Handedness was assessed by measuring the grasp-reflex strengths from the right and left hands in 10 trials from each hand alternatively. There were two handedness groups: right-handers (R-L significantly greater than zero) and left-handers (significantly smaller than zero). Contrary to the GBG model, the mean free T concentration was found to be significantly higher in right-handers than left-handers for males and females. There was no significant difference in the total T levels between right- and left-handers. Free T concentrations positively correlated with RL grasp-reflex strengths, i.e. right-handedness increased as T increased, and left-handedness increased as T decreased. Contrary to these positive correlations, T negatively correlated with the grasp-reflex strengths from the right and left hands. These results partly supported the GBG hypothesis for this spinal-motor-asymmetry model. Total T did not significantly correlate with grasp-reflex strengths. The results suggest that prenatal T may at least play a role in prenatal determination of spinal motor lateralisation, with a possible consequent upward regulation of cerebral lateralisation.

Journal Article↗

PubMed2001

Hand preference in Italian students.

Italian undergraduates (N = 2326) were administered the Italian revised version of Edinburgh Handedness Inventory (Salmaso & Longoni, 1985). Left-handedness was documented in relation to sex, university faculty, geographic origin and handedness pressure. A greater proportion (7.9%) of left-handedness was found compared to previous works on Italian samples. Additional results indicated a difference in left-handedness incidence among Southern, Central and Northern Italian regions. Results are discussed in terms of social and cultural influence.

Journal Article↗

PubMed2005

Laterality in five-year-olds conceived by intracytoplasmic sperm injection, standard in vitro fertilisation and natural conception: a European study.

OBJECTIVE: To assess laterality in a group of European children conceived with the help of assisted reproductive therapy, or naturally conceived. DESIGN: Prospective cohort study. SETTING: Five European countries. POPULATION: A total of 1525 five-year-old children divided into three groups according to conception status: naturally conceived; intracytoplasmic sperm injection (ICSI); in vitro fertilisation (IVF) group. METHODS: All children were assessed using the McCarthy Scale of Children's Abilities (Motor Scale) with additional items using a comb, a spoon and an indirect measure was made of the parental handedness scores, using a questionnaire. MAIN OUTCOME MEASURES: Child handedness for drawing and writing. RESULTS: Observed handedness did not differ significantly between natural conception, IVF and ICSI in girls or boys, except for ICSI-conceived girls, fewer of whom were left-handed than the naturally conceived controls, 7.0%versus 12.4% (P < 0.05), however, this was close to the population norm of 8%. The degree of parental handedness did not significantly vary in the three groups. CONCLUSIONS: Laterality, as assessed by handedness, may be marginally less common in girls conceived with assisted reproductive therapies than with children conceived naturally.

Adult↗

PubMed1976

The search for cerebral dominance in monkeys.

Twelve monkeys with statistically significant and consistent manual preferences on three handedness tests were subjected to unilateral ablations in the association cortex. Eight received lesions in the foveal prestriate cortex, and four lesions in the dorsolateral frontal cortex; half the subjects in each group were operated on the dominant, and half on the nondominant hemisphere for handedness. The unilateral posterior preparations were significantly inferior to the control group of four unilateral frontals and five sham operated monkeys on three series of visual pattern discrimination problems. No evidence was obtained that lesions in the nondominant hemisphere. The results of this and four other experiments indicate that there is no cerebral dominance for problem-solving in monkeys. Recent research indicates that handedness in rhesus monkeys is only superficially similar to handedness in humans; thus, monkeys appear to lack cerebral dominance for handedness as well as for cognitive behavior.

Animals↗

PubMed1982

Differences between two studies of hand preference in psychiatric patients.

Significant differences in handedness patterns between groups of psychiatric patients and normal controls were identified in two recent British studies, with substantial disagreement in some important findings. Most of the discrepancies were attributable to the different application of a simple classification of handedness data, and the remainder to differences in sample size. Diagnosis, sex and age were then found to have a similar effect on handedness in both studies. Neurotic patients were similar to controls regardless of classification, whereas mixed handedness in personality disorder depended on it. There was no overall excess of left-handedness among schizophrenics, but trends towards excess sinistrality in men and fully dextrality in women approached significance.

Adolescent↗

PubMed2005

Laterality of motor control revisited: directionality of callosal traffic and its rehabilitative implications.

Based on evidence derived from personal data and a comprehensive review of the literature, this article provides a perspective of laterality of motor control in humans. The evidence supports existence of directionality in callosal traffic, codified in handedness. However, it is the neural handedness that definitively reveals the directionality of signal traffic between the executive and the minor hemisphere; the minor hemisphere is devoted to the affairs occurring on or toward the nondominant side of the body. Thus, moving the nondominant side of the body (and sensing from it) are bi-hemispherical events that require callosal participation. Time-resolved data are provided that indicate the absence of any ipsilateral corticospinal tract innervation in humans. The rehabilitative aspects of the new circuitry (i.e., one-way callosal traffic scheme) is reviewed, establishing that previously described plasticity or reorganization of cortical structure was a reflection of the newly described anatomy underpinning handedness. The distinction between neural and behavioral handedness is emphasized, suggesting simple and robust ways to establish a person's handedness without resorting to invasive and inconclusive tests currently in vogue. In the past, lack of knowledge of directionality in callosal traffic has resulted in surgical removal of healthy hemispheres (including the major hemisphere) in futile attempts to stop epilepsy in those with an intractable condition. Evidence is provided for lack of any motor communication from the minor to the major hemisphere, which makes the minor hemisphere incapable of initiating and propagating seizures.

Brain Mapping↗

PubMed1988

The distribution of hand preference in normal men and women.

The distributions of the hand preferences (Geschwind scores) were studied in men and women. The incidences of the right-, mixed-, and left-handers were 66.1, 30.5, and 3.4%, respectively. The left- and right-handers (LHs, RHs) were represented by two bars located at the opposite ends of a J-shaped histogram for the total sample, men, and women. The distributions for the total RHs, and male RHs were not J-shaped, but negatively skewed, the mode being close to the mean. The frequencies for the females increased linearly. The distributions for the LHs did not significantly deviate from normality. Except for the LHs, the percentage distributions of the Geschwind scores were J-shaped. The LHs were evenly distributed by chance to be expected in a random sample from a rectangular population. The incidence of weak right-handedness was significantly higher in men than women. The total RHs were more lateralized than the total LHs who showed a tendency toward weak left-handedness. In males, the incidence for weak left-handedness was significantly higher than that for strong left-handedness. The opposite was established for females. The probability of the consistent right-handedness was significantly higher in women than men. The LHs were less lateralized, and more widely dispersed than the RHs. The statistical analysis of the distributions indicated that females tended to be more lateralized, i.e., more right-handed, and more left-handed, than males.

Adult↗

PubMed1993

Normal distribution of hand preference and its bimodality.

The distribution of hand preference was studied in human subjects by means of The Waterloo Handedness Questionnaire and Edinburgh Handedness Inventory. The Waterloo Handedness scores (WS) and Geschwind Scores (GS) were estimated. Left-handers (WS < 0; GS < 0) and right-handers (WS > 0; GS > 0) constituted separate groups (dichotomy). The WSs, and to a lesser extent GSs, were distributed normally when only the right-handers were considered. There was a significant positive-linear correlation between WSs and GSs. These results suggested that a detailed questionnaire such as the Waterloo Handedness Questionnaire would be more appropriate than concise questionnaires in assessing hand preference. A normally distributed right-hand preference and a widely dispersed left-hand preference also supports the concept of anomalous dominance for left-handedness.

Adolescent↗

PubMed2004

Coerced training of the nondominant hand resulting in cortical reorganization: a high-field functional magnetic resonance imaging study.

OBJECT: The authors investigated brain strategies associated with hand use in an attempt to clarify genetic and nongenetic factors influencing handedness by using high-field functional magnetic resonance imaging. METHODS: Three groups of patients were studied. The first two groups comprised individuals in whom handedness developed spontaneously (right-handed and left-handed groups). The third group comprised individuals who were coercively trained to use the right hand and developed mixed handedness, referred to here as trained ambidexterity. All trained ambidextrous volunteers were certain that they were innately left-handed, but due to social pressure had modified their preferred hand use for certain tasks common to the right hand. Although right-handed and left-handed volunteers displayed virtually identical cortical activation, involving homologous cortex primarily located contralateral to the hand motion, trained ambidextrous volunteers exhibited a clearly unique activation pattern. During right-handed motion, motor areas in both hemispheres were activated in these volunteers. During left-handed motion, the right supplemental motor area and the right intermediate zone of the anterior cerebellar lobe were activated significantly more frequently than observed in naturally right-handed or left-handed volunteers. CONCLUSIONS: The results provide strong evidence that cortical organization of spontaneously developed right- and left-handedness involves homologous cortex primarily located contralateral to the hand motion, and this organization is likely to be prenatally determined. By contrast, coerced training of the nondominant hand during the early stages of an individual's development results in mixed handedness (trained ambidexterity), indicating cortical reorganization.

Cerebral Cortex↗

PubMed2004

Verbal dichotic listening in developmental stuttering: subgroups with atypical auditory processing.

OBJECTIVE: The major aim of this study was to determine whether adults with persistent developmental stuttering have atypical auditory processing. BACKGROUND: Stuttering has been attributed to aberrant hemispheric dominance, and auditory processing deficits have been found in some adults who stutter. Dichotic listening, an indirect measure of auditory processing, has not been used to study auditory laterality in right- and left-handers who stutter. Because left-handers and people who stutter may have aberrant hemispheric dominance, it is important to examine auditory neural systems in right- and left-handed people who do and do not stutter. METHODS: Adults with persistent developmental stuttering (n = 18) and matched controls (n = 28) were studied by simultaneous binaural (dichotic) presentation of consonant-vowel stimuli in three attention conditions: nondirected attention, attention directed right, and attention directed left. Sex-handedness groups (stutter and control) included right-handed men and women and left-handed men, but not left-handed women because this stutter subgroup could not be recruited. To study ear advantage and auditory laterality, two dependent measures were examined: percent left and right ear responses and lateralization shift magnitude. Potential relationships between degree of handedness and dichotic listening measures were also examined. RESULTS: Matched controls and right-handed men who stutter had the expected right-ear advantage (REA) in the nondirected attention condition. In contrast, left-handed men who stutter had a left-ear advantage (LEA), and right-handed women who stutter did not have a lateral ear bias in the nondirected attention condition. Right-handed women who stutter had the greatest tendency to hear a sound that was not presented to either ear, and were relatively unable to selectively direct attention left or right. In contrast, left-handed men who stutter were able to shift attention to the left and right ear better than any other group. For the fluent control group, there were no significant relationships among degree of handedness and dichotic-listening variables. For the stutter group, degree of handedness was significantly related to percentage left and right ear response and to the lateralization shift magnitude. CONCLUSIONS: Left-handed men who stutter and right-handed women who stutter have atypical auditory processing but differ in important ways. The left-ear bias found in left-handed men who stutter in the nondirected attention condition suggests that their right temporal lobe may be important in perceiving speech, and, therefore, they have mixed dominance. These subjects were also better at shifting attention in both directions in comparison to all other groups; thus, the right hemisphere, which is dominant for shifting attention to both right and left space, may be activated. In contrast, the right-handed women who stutter had no ear bias in the nondirected attention condition, made more perceptual errors, and had difficulty shifting attention to the left and right. Although these results suggest that right-handed women who stutter have attentional deficits, the relationship between attentional disorders and stuttering remains to be elucidated. Because right-handed men who stutter were not different from controls, aberrant hemispheric dominance cannot fully account for stuttering. Unfortunately, left-handed women were not examined in this study. Therefore, these interesting sex-handedness effects found in left-handed men and right-handed women who stutter must be interpreted with caution.

Adult↗

PubMed1981

Earedness (ear choice in monaural tasks): its measurement and relationship to other lateral preferences.

A total of 373 normal young adult subjects were distributed among 5 experiments measuring earedness. Handedness, eyedness and familial L-handedness were also indexed. Special care was taken to remove environmental asymmetries when determining ear preference when listening to sound from a suspended earphone, and from a stopwatch on a table, and for using a telephone symmetrically constructed and displayed. Ear preference was strongly influenced by seemingly minor environmental asymmetries and did not influence telephone habits, and must be considered a very weak lateral preference. Earedness was as concordant with handedness as eyedness was found to be; earedness was concordant with handedness in 74% of dextrals and 65% of sinistrals, but earedness was not related to eyedness. Earedness did not vary with putatively hemisphere-specific stimulus types (music, speech). Laterality of telephone use was jointly determined by handedness and the expectation of writing, not by earedness.

Adult↗

PubMed1998

Major review: ocular sighting dominance: a review and a study of athletic proficiency and eye-hand dominance in a collegiate baseball team.

PURPOSE REVIEW: Laterality preference in sensory and motor functions of symmetrically disposed organisms have been studied for centuries. The relation between handedness and the eyes and vision (ocular sighting dominance) has been a focal point despite their physiologic dissimilarity. STUDY: To examine a college varsity baseball team for handedness and ocular sighting dominance to determine if their patterns of eye-hand dominance differed from the normal population and/or contributed to their individual relative success compared to their peers. Specifically: whether crossed eye- hand dominance favors the batter and uncrossed eye-hand dominance favors the pitcher. SUBJECTS AND METHODS: Twenty five UF varsity players were examined. All were male. Their visual acuity, stereoscopic vision, ocular motility and ocular sighting dominance were determined, the last by a pointing test which allowed the diagnosis of a central form of ocular dominance, but was not per se affected by handedness. Handedness was determined by preferred arm for throwing or hitting. No subject was ambidextrous. A control population was established consisting of the first 100 consecutive adults seen by the first author in the UF Eye Center with 20/20 vision O.U. and a normal eye exam. RESULTS: The control group displayed eye-hand dominance patterns similar to those previously reported in the literature for the general population. In the experimental group of baseball players, the incidence of conventionally predominant (in normals) ipsilateral or uncrossed eye-hand dominance was much lower (39%) than the normal control population (65%). The incidence of contralateral or crossed eye- hand dominance was 35%, twice that of the normal control population (18%) (p<0.01). The incidence of central ocular dominance with right or left handedness was 26% or 50% higher than a normal control population (17%) (p<0.25). With regard to individual performance, those players with central ocular dominance, whether right or left handed, were the most successful players in both pitching and batting. Pitchers who were uncrossed eye-hand dominant were distinctly more successful than crossed. Batters who were crossed eye-hand dominant were slightly more successful than uncrossed. CONCLUSIONS: The pattern of eye-hand dominance appears related to athletic proficiency for baseball. Warning: Note well: This information may be useful in career guidance but does not justify or medically indicate attempts to alter ocular sighting dominance or eye-hand dominance patterns as these are determined probably genetically or at such an early age that they cannot be successfully altered later. Attempts to so alter them are historically fraught with irremediable psychological or physical injury to the subject, including permanent incapacitating double vision.

Adult↗

PubMed2006

The manifestation of infant hand-use preferences when reaching for objects during the seven--to thirteen-month age period.

Handedness is an aspect of hemispheric specialization whose pattern of expression may signal an unusual specialization that in turn, may underlie several developmental psychopathologies. It is generally believed that infant handedness is neither stable nor reliable and hence, cannot be used as an early marker of potential developmental abnormality of hemispheric specialization. We show that infant hand-use preferences for apprehending objects can be reliably assessed and may be relatively stable throughout the 7-13 month age period. However, the results also demonstrate that identifying infant handedness requires assessment using very large sample sizes with multiple assessment periods because it is likely that there may be many more than three patterns in the development of handedness during infancy.

Age Factors↗

PubMed1995

Diverging asymmetries of temporo-parietal cortical areas: a reappraisal of Geschwind/Galaburda theory.

The general theory on the biological foundations of cerebral dominance formulated in 1985 by Geschwind and Galaburda entirely relies on a postulated causal relationship between anatomical asymmetry of the planum temporale and functional lateralization of the human brain, but does not take into account asymmetry of another cortical region, the parietal operculum. In 40 normal volunteers whose handedness was specified by the Edinburgh Handedness Inventory, we assessed asymmetries of these two regions on MRI sagittal scans. For both measurements, a significantly larger leftward asymmetry was found in the 24 consistent right-handers compared to the 16 non-right-handers. Moreover, the combination, for each subject, of the two indices of asymmetry, yielded four different subtypes between which handedness distribution significantly differed. We conclude that planum temporale and parietal operculum asymmetries may be divergent and that their convergence is strongly associated with right-handedness. Functional and developmental implications of these findings are discussed by reference to the Geschwind/Galaburda theory.

Adolescent↗

PubMed1981

Hand usage in a colony of bonnet monkeys, Macaca radiata.

Handedness and its possible inheritance have been studied in a colony of 69 Macaca radiata by observation of hand usage during daily feeding and foraging activities. Each animal was observed for the number of right- and left-handed actions made during two tasks:feeding and searching. Individual animals fell into one of three classes: significantly right-handed, significantly left-handed, and no significant preference. For analysis, handedness was considered as both a directional phenomenon (percentage right-handed usage) and a degree phenomenon (absolute deviation from 50:50 hand usage). Feeding and searching were significantly correlated for both direction and degree. Therefore, laterality for handedness does exist in this primate species. A developmental aspect to laterality was suggested by the positive correlation of degree with age. No mother-offspring correlations were found for either direction or degree and half-sibships were not more similar for either. Thus, there is no evidence for a genetic component to either direction or degree of handedness.

Age Factors↗